1. Field of the Invention
The present invention relates to a filter for a low-pressure mercury vapor lamp.
2. Prior Art
In recent years, low-pressure mercury vapor lamps have been used as a light-source for a photo-CVD, photo etching, etc.
Such lamps have emission lines of 185 and 254 nm in wave-length and, when only radiation of 185 nm should be used for particular applications in a photo-CVD, photo etching, etc. filters coated with a dielectric layer have been used for filtering 254 nm radiation. However, since such filters have limitations with respect to their size originating from limitations related to the coating installation, large-size filters are hardly available. Even though large-size filters are available through special coating installation, they are extremely expensive. Further, they have a drawback in that they quickly deteriorate since they absorb ultraviolet radiation.